Apparatus for cyclic pellet impact drilling



2 Sheets-Sheet 1 l 7 5 m ik M W., Sept. 4, 1956 1 w. LEDGERWOOD, .1R gAPPARATUS FOR CYCLIC PELLET IMPACT DRILLING Filed March e, 1952 Sept. 4,1956 l.. w. LEDGERwooD, 1R 2,761,651

APPARATUS FOR cYcLrc PELLET IMPACT DRILLING Filed March 6, 1952 2Sheets-Sheet 2 United States Patent O APPARATUS FOR CYCLIC PELLET IMPACTDRILLING Leroy W. Ledgerwood, Jr., Tulsa, Okla., assigner to EssoResearch and Engineering Company, a corporation of Delaware ApplicationMarch 6, 1952, Serial No. 275,171

4 Claims. (Cl. 255-61) This invention concerns a novel technique ofdrilling bore holes in the earth. The invention embodies the basicprinciples of drilling employed in the so-called `pellet impact drillingmethod. Thus, a stream of high velocity directed pellets is employed topulverize the earth so as to drill or cut a bore hole. In accordancewith this invention, means and apparatus are disclosed for maintainingthe drill ejecting the pellets at a desired spaced distance from thebottom of `the borehole. The invention employs the concept of using acyclic drilling operation in accordance with which the drill is normallymaintained at a spaced distance from the bottom of the bore hole.Periodically, however, the drill is lowered to the bottom and is thenretracted a set distance from the bottom to permit periodically feelingfor and readjusting the displacement of the drill from the bottom of thcbore hole.

The basic principles of pellet impact drilling are fundamentally simple.Means are simply required to provide a jet of high velocity fluidincluding provision for entraining and accelera-ting pellets in this jetof fluid. The basic principles of the technique of drilling by pelletimpact are set forth in co-pending applications, Ser. No. 268,873 ofPhilip S. Williams, entitled Pellet Impact Drilling Method andApparatus, and Ser. No. 268,882 of Leroy W. Ledgerwood, Jr., entitledMomentum Pellet Impact Drilling Apparatus, both applications iiled onJanuary 29, 1952.

Basically the pellet impact technique for drilling bore holes in theearth involves the use of a stream of fluid pumped from the surface ofthe earth through a tubular member to a jet nozzle assembly adjacent thebottom of the bore hole. The jet nozzle assembly is adapted to direct ahigh velocity jet of uid against the formation being drilled and isprovided with means for entraining in the jetted fluid a multitude ofpellets which are accelerated to high velocity in the jet stream andthereby acquire considerable kinetic energy so that when the pelletsimpinge against the formation the resulting percussive and fracturingforces exert a drilling action. Preferably the pellets that are employedare smooth, non-abrasive and esentially sperical and are of substantialsize, preferably in the size range of about l to about l in diameter. ltis preferred that hard, tough metallic alloys be employed as the pelletmaterial.

It is generally desirable in obtaining a suitable ejection of pellets toemploy a nozzle assembly utilizing a primary and secondary jet nozzle.The primary nozzle is employed to convert uid pumping pressure tovelocity energy. Consequently, fluid pumped through the primary nozzleis subjected to a substantial pressure drop, of 100 pounds per squareinch or more, to provide a constricted directed high velocity jet offluid. A secondary nozzle is positioned immediately below and concentricwith the primary nozzle. The secondary nozzle should have asubstantially greater diameter than the primary nozzle to accommodatethe total volume of uid from the primary nozzle in addition to thevolume of pellets there entrained. This configuration and arrangement ofnozzles, by its nature, creates an aspirating eifect which plays a partin the recirculation of the pellets.

By the nature of pellet impact drilling of the character described, itis necessary that the jet nozzle assembly used for ejecting the pelletsbe maintained above the bottom of the bore hole. It is generallyundesirable to have any portion of lthe drill extending below the nozzleassembly as circulation of the pellets would cause rapid wear of thisportion of the drill. Thus it is generally undesirable to employmechanical standoff arrangements to position the jet nozzle assembly atthe desired distance above the bottom of the bore hole. It is theprincipal object of this invention to provide a method and apparatus forspacing the drill from the bottom of the bore hole without necessitatingconstant contact of any portion of the drill with the bottom of the borehole.

The method by which this is achieved depends upon periodically loweringthe drill so as to contact the bottom of bore hole. By then retractingthe drill a selected amount, normal drilling can be conducted at theoptimum displacement of the drill from bottom. The cyclic operation ofbringing the drill in contact with bottom need only infrequently beconducted so that a small portion of the drilling time is required forthis positioning operation. Apparatus embodying this method may best beconstructed so as to maintain the drill itself in sliding relation withthe lower termination of the drill string.

This sleeve arrangement may be provided with accessory means toautomatically and periodically cause the sleeve supported drill tocontact bottom and to retract from the bottom so as to maintain thedesired displacement of the drill.

A preferred embodiment of the invention is illustrated in theaccompanying drawings in which:

Figure 1 illustrates in cross-sectional elevational detail the drill ofthis invention in drilling position;

Figure 2 is a cross-sectional view of Figure l along the line II-II;

Figure 3 is a cross-sectional view of the drill of Figure 1 along theline III-III of Figure 1;

Figure 4 is a cross-sectional view of the drill of Figure l along theline of IV-IV; and nally Figure 5 is an enlarged detail cross-sectionaldrawing of the trigger valve arrangement employed to cause automaticcycling operation of the drill assembly of Figure 1.

Referring to these drawings, it will be seen that the entire drill issupported by a tubular member which may constitute a drill stringidentified by numeral 1. The drill itself constitutes a primary nozzle 3and a secondary nozzle 9 of the character hereinbefore identified. Theprimary nozzle 3 may be fixed to and constitute the lower termination ofa sleeve element 2 which is maintained in sliding relation with thelower termination of the drill string 1. The secondary nozzle 9 issupported below and coaxial to the primary nozzle 3 by means of thesupport elements 25 which may be fixed to either the sleeve 2 or theprimary nozzle 3.

A cylinder 17 is xed to the drill string 1 immediately above theuppermost position of sleeve 2. This cylinder extends downwardly alongdrill string 1 about sleeve element 2. The lower portion of the cylinderis maintained in fluid-tight sliding relation with sleeve member 2 bythe provision of packing 26. A piston 4 is provided on the uppertermination of sleeve 2 within the cylinder member 17. A fluid passageextends from the interior of the drill string 1 through the wall of thecylinder to the interior of the cylinder near the bottom thereof. Thispassage is identified by number 6, and preferably terminates in an oriceopening 7. If desired, a number of such passages may be provided.

In addition to these elements, an elongated slot 13 is provided in thewall of the tubular support member 1 at the portion of the drill stringover which sleeve 2 may slide. One or more ports 14 are cut throughsleeve element 2 which are normally not in register with slot 13 and maynormally be somewhat above the upper termination of slot 13. Finally,one or more ports 27 are cut through an upper portion of the cylinder17.

From this brief identification of the principal elements of the drillillustrated, the operation of this apparatus may be understood. In thecourse of the description of the operation reference will be made to theremaining features of construction not heretofore described.

The drill is normally maintained in the condition and positionillustrated in Figure l. Drilling fluid is pumped through the drillstring 1 to be ejected from primary nozzle 3 and to pass downwardlythrough secondary nozzle 9. Pellets are entrained in the secondarynozzle and are accelerated and directed downwardly through the secondarynozzle so as to impinge against the bottom of the bore hole. Thesepellets rebounding from the bottom of the bore hole are carriedoutwardly and upwardly in the ow of drilling fluid in an annular channelbetween the bore hole and the external portion of secondary nozzle 9.Immediately above the secondary nozzle 9 an enlarged annular space isprovided causing the fluid to have a substantially reduced verticalvelocity. Consequently, immediately above the secondary nozzle 9 pelletsmay settle from uptlowing drilling fluid so as to drop downwardly intothe interior of the secondary nozzle for recirculation as described.This recirculation of the pellets is facilitated by aspiration forcescreated by this nozzle arrangement. Drilling fluid will pass upwardly tothe surface of the earth for recirculation through the interior of thedrill string.

The propulsion of drilling uid through nozzle 3 and nozzle 9 willmaintain a net downward force on these elements. This force, in additionto the weight of nozzle 9 and the slidable elements supporting it, willcreate a normal tendency for extension of the sleeve arrangementprovided so as to normally urge the nozzle arrangement downwardlyagainst the bottom of the bore hole. This downward force is counteractedand overcome by an upward force provided by the cylinder and pistonarrangement employed.

Thus drilling lluid under the pumping pressure employed is at all timesforced from the interior of the drill string through channel 6 andorifice 7 into the cylinder so as to act upwardly against piston 4. Thisupward force is proportioned by design considerations so as to normallyovercome the downward forces on the nozzle arrangement so as to maintainsleeve 2 in the upward position illustrated. ln the practicalconstruction of this apparatus, the area of piston 4 may be chosen sothat when the pressure in the annular chamber 5 within the cylinder isat least about 1/2 the pressure in the drill string, sufficient upwardforce will be exerted by the piston arrangement to balance the netdownward force on the nozzle assembly. As a result circulation ofdrilling uid through passage 6 to the interior of the cylinder willnormally maintain sleeve 2 in its uppermost drilling position as shown.

To permit the desired cyclic operation causing lowering of the nozzleassembly to the bottom of the bore hole a trigger arrangement isemployed. This trigger arrangement serves to rapidly and sharply reducethe pressure within the annular space 5 of the cylinder so as to permitpiston 4, sleeve 2 and the associated elements to drop downwardly. Forthis purpose it is necessary to provide a pressure release mechanism incylinder 5 which will operate to reduce the pressure therein at periodicintervals. One means by which this may be accomplished is illustrated inFigure l and is particularly shown in Figure 5. The method employeddepends upon the gradual build-up of pressure within the annular space 5permitted by the restricted orifice 7. Orifice 7 permits only a limitedamount of uid to pass from the drill string into the cylinder, so that atime period of live minutes for example, may be required for thepressure to build up within the annular space 5 to the pressure of thefluid within the drill string. The pressure release mechanism isarranged to permit opening of a valve 8 when this pressure has built upto substantially the pressure within the drill string. The pressurerelease mechanism operates independently of the relative position ofpiston 4 within the cylinder 17.

The rapid release of pressure within the annular space 5 occurs througha valve opening 28 which may be cut in piston 4. This valve opening isnormally closed by valve member 8 which sets on port 28. A valve stem 10xed to the valve member 8 extends downwardly in conjunction with adetent arrangement adapted to normally hold valve 8 in closed position.As illustrated in Figure 5 the detent may constitute a recess cut intostem 10 which receives a ball 11 urged into detent position by spring29. A second spring element 12 is maintained in compression above valvemember 8 acting to apply a force to maintain valve member 8 in sealedposition. This arrangement is constructed so that substantially greaterupward force is required on valve 8 to unseat the ball detent 11, thanto` compress spring 12. Thus, once fluid pressure builds up withinchamber 5 to the pressure of uid in the drill string, suflicient forcewill be exerted on valve 8 to unseat the detent arrangement, and topermit opening of the valve. As spring 12 is relatively weak, the valvewill stay open as long as Huid flows through the valve. This uid ow willcontinue until pressure within annular chamber 5 is equal to pressure inthe annular space between the bore hole and the drill string;equalization occurring through port 27. When fluid flow stops, thenspring 12 is able to force valve 8 back on its seat permittingre-engagement of the detent 11, and preventing the valve from openingagain until a very high fluid pressure is reached below valve 8.

This arrangement therefore serves to provide the desired triggering ofthe sleeve arrangement. Normally, uid will pass through channel 6 andorifice 7 to apply pressure within annular chamber 5 so as to maintainthe piston in the uppermost position. The piston will remain in theuppermost position during the time period required for fluid to leakthrough orice 7 to raise the pressure within annulus 5, to the pressurewithin the drill string. When this happens, valve 8 is triggered tocause rapid release of pressure and to permit the nozzle assembly todrop downwardly to contact the bottom of the bore hole. Preferably,particular provisions are made to secure the rapid retraction of thedrill bit from thc lowermost position to the position illustrated in thedrawing. This depends upon utilization of slot 13 and port 14 alreadyidentified. When the drill nozzle assembly has contacted the bottom ofthe borehole, contact with the bottom will prevent rotation of thenozzles and the sleeve element 2. Continued slow rotation of drillstring 1 from the surface of the earth will therefore cause drill string1 to rotate within sleeve 2. This rotation will bring port 14 of sleeve2 in register with slot 13 of the drill string. When this happens a uidpassage is opened from the interior of the drill string to the annularchamber 5 so as to cause a rapid increase of pressure within chamber 5forcing piston 4 upwardly to lift the drill bit off the bottom. Thisupward movement will be rapid because of the large size ports employed.Upward movement of the bit will continue until pin 15 which is fixed indrill string 1 is engaged by the upward moving cam 16 which is rigidlyxed to the upper surface of piston 4. Contact of the pin 15 with the cam16 will force rotational movement of sleeve 2 with respect to thetubular support or drill string 1. This rotational movement will forceslot 13 and port 14 out of register. The elements described are soarranged that this occurs when the lower termination of drill string 1seats on shoulder 18 provided adjacent the primary nozzle 3. Thereafterthe cyclic operation continues with the gradual build-up of pressure dueto fluid passage through channel 6 and orifice 7.

It is apparent that the different operational steps conducted on acyclic basis may be adjusted as desired by design of the elementsemployed. Thus it is practical to maintain the bit in a stationaryposition off bottom for about five-sixths of the total time cycle, whilemoving downwardly to contact bottom and to be retracted there from forthe other one-sixth of the time. Division of time between theseoperations may be adjusted by choice of orifice and port sizes and theirrelative positions.

It is a particular feature of the apparatus illustrated that one or moreports 19 cut through sleeve 2 are positioned to provide hydraulicinformation as to the distance of the drill bit from the bottom of thebore hole. Thus, when sleeve 2 and the nozzle assembly is permitted todrop downwardly, port 19 may be at a position below the lowertermination of drill string 1, if the drill bit was originally at anundesired distance above the bottom of the bore hole. If port 19 doesdrop beyond this point, there will be a release of pressure within thedrill string by the passage of fluid through port 19 which will informan operator at the surface of the earth that this limiting position hasbeen reached. This provides a convenient indication that it is necessaryto lower drill string 1 a short distance to maintain the desiredpositioning of the drill bit.

In using this apparatus it is generally preferred that the drill stringbe continuously lowered at a rate somewhat less than the normal drillingrate of the apparatus. Progression of the drilling at a rate faster thanthat at which the drill string is lowered will eventually result in thepressure drop referred to through port 19 when the drill is in thebottom contacting position. When this happens an operator will thenlower the entire drill string a limited amount and will then resume thecontinuous lowering at the rate referred to. Alternatively, if desired,the drill string can be maintained stationary except when port 19operates to permit release of pressure. When this occurs the drillstring will simply be lowered an incremental amount and drillingcontinued until port 19 is again opened by the cyclic operation.

It should be observed that all elements of the apparatrs describedoperate on the basis of pressure differentials existing in the differentportions of the apparatus and the bore hole. None of the elementsdescribed depends upon absolute pressures and consequently changes instatic pressure within the bore hole, even though at great depth, willnot affect the operation of the apparatus.

It is apparent that arrangements other than those disclosed may beemployed to secure the cyclic drilling referred to.

What is claimed is:

1. A drilling apparatus comprising in combination a tubular supportmember and a sleeve member maintained in vertical telescopic slidingrelationship, a nozzle element supported on the lower termination ofsaid sleeve, a cylinder fixed to one of said members, a piston fixed tothe other of said members and positioned within said cylinder, a uidpassage extending from the inner bore of one of said members to withinthe portion of said cylinder that will exert a lifting force on saidsleeve when fluid pressure is built up within said cylinder, and apressure release mechanism operative to release pressure within saidcylinder sharply when a predetermined pressure has been built up withinsaid cylinder, whereby when fluid pressure exists within said tubularsupport and sleeve members, pressure will periodically build up withinsaid cylinder and will periodically be released by said valve, thusimparting a vertical reciprocating motion to said sleeve, said pressurerelease mechanism comprising a valve member having a valve passage and avalve closure element, a first spring element urging said valve closureelement to seal in said valve passage, a detent member acting to retainsaid valve closure member in sealed position, and a second springelement urging said detent member against the valve closure member.

2. A drilling apparatus comprising in combination a tubular member and asleeve member maintained in vertical telescopic sliding relationship, ajet nozzle assembly supported by said sleeve below said tubular member,an annular cylinder fixed to one of said members and encircling theother member in fluid-tight sliding relationship, an annular pistonfixed to the other of said members in fluid-tight sliding relationshipwith the inner wall of said annular cylinder, a uid passage extendingfrom the inner bore of one of said members to within the portion of saidcylinder that will exert a lifting force on said sleeve when fluidpressure is built up within said cylinder, and a pressure releasemechanism operative to release fluid pressures within said cylinderrapidly when a predetermined pressure has been built up within. saidcylinder, whereby when fluid pressure exists within said tubular supportand sleeve members pressure will periodically build up within saidcylinder and will periodically be released by said valve, thus impartinga vertical reciprocating motion to said sleeve, said pressure releasemechanism comprising a valve member having a valve passage an-d a valveclosure element, a first spring element urging said valve closureelement t-o seal in said valve passage, a detent member acting to retainsaid valve closure member in sealed position, and a second springelement urging said detent member against the valve closure member.

3. The apparatus defined by claim l including a vertical slot in saidsupport member and at least one perforation in said sleeve memberadapted to register with said slot on relative rotation of said sleeveand support members.

4. The apparatus defined by claim 3 including a cooperat-ing cam elementand cam follower fixed` to. said sleeve member and said support memberurging rotation of said sleeve relative to said support member when saidsleeve member is forced upwardly with respect to said support member.

References Cited in the file of this patent UNITED STATES PATENTS1,502,851 Gale July 29, 1924 1,659,826 Malloy et al. Feb. 21, 19281,669,130 Jensen May 8, 1928 1,927,836 Kightlinger Sept. 26, 19332,233,260 Hawthorne Feb. 25, 1941 2,422,031 Merten June 10, 19472,448,459 Palm Aug. 31, 1948

1. A DRILLING APPARATUS COMPRISING IN COMBINATION A TUBULAR SUPPORTMEMBER AND A SLEEVE MEMBER MAINTAINED IN VERTICAL TELESCOPIC SLIDINGRELATIONSHIP, A NOZZLE ELEMENT SUPPORTED ON THE LOWER TERMINATION OFSAID SLEEVE, A CYLINDER FIXED TO ONE OF SAID MEMBERS, A PISTON